1. Field of the Invention
The invention relates to a process for manufacturing tubular shaped plastic ink reservoir cartridges, which may be injection molded. The cartridges may be placed on top of a writing instrument or may be inserted into a writing instrument. Upon attachment or insertion, the sealing element of the cartridge is destroyed, or at least penetrated, at an assigned breaking point. This breaking point is designed to be of a thinner material strength.
2. Description of Prior Art
West German DT-PS 1 274 928 is an example of this type of ink cartridge, and they are generally manufactured in an injection molding process. In order to produce, simultaneously, by means of the injection process also the preset breaking points, in the cartridge sealing element, the injection mold die must be able to form regions of thinner material strength which can make leakproof seals between the sealing element and the remaining part of the ink cartridge containing the ink reservoir chamber. However, in the case of injection molding, and also in other processes used in the manufacturing of ink cartridges, one encounters relatively large variations in tolerances. Therefore it is necessary that in the area of the reduced material strength, a certain minimum thickness is provided so that even in case of large tolerance fluctuations, the tight seal of the ink reservoir chamber remains assured.
Conventionally, there is a necessity for adhering to the lower limit in respect to material thickness in manufacture by injection molding, wherein predetermined breaking points are obtained which can only be penetrated by the use of large amounts of energy. In the case of conventional ink cartridges, the tearing forces or penetration forces required for severing the breaking points are on the order of 6 kp to 12 kp.
In order to avoid a high rejection rate because of insufficient seal in the preset breaking point area, in the manufacture of ink cartridges by the aforementioned process, it is necessary that the user must apply relatively large amounts of energy or force in order to open the flow exits by rupturing the preset breaking points in the sealing element.